1. Field of the Invention
The present invention relates to a weight compensating device comprising a carrier and a component which is supported on the carrier and is displaceable particularly in a vertical direction by means of a drive.
2. Background Information
Especially in the field of machine tools, components which are in part relatively heavy must be displaced and/or precisely held in vertical direction against their weight or against gravity.
Many mechanisms are already known wherein a weight compensating device is used for compensating at least part of the weight/gravity of the component and for relieving the drive at the same time. The solutions include, for instance, counterweights, which are e.g. held via a deflection pulley and a rope, or the like. Further mechanisms show hydraulic or pneumatic solutions.
The already known solutions are marked by the drawback that the sum of the masses to be moved will be increased considerably when a counterweight is used because the mass of the weight compensating device has to be added to the mass of the component.
The total mass which is increased on the whole entails serious problems with respect to the inertia of the component. For instance, it is not possible to move accelerations of more than 1 g because this will otherwise damage the weight compensating device or impair its functional reliability. In particular, cables or the like, used by the weight compensating device, cannot be held under tension for a long period of time.
Further problems are created by accelerations that arise and necessary decelerations.
In hydraulic and pneumatic solutions, additional friction is caused by the use of hydraulic cylinders or pneumatic cylinders during movement of the component. This additional friction must be compensated by the drive. Additional friction arises on account of the piston seals of such piston/cylinder arrangements.
Hence, the overall problem arises that, upon a directional reversal of the movement of the component, frictional forces have to be overcome that are quite considerable, and that large additional masses have to be accelerated and decelerated, respectively.
Especially in machine tools in which three-dimensional operating movements are to be created, this results in undesired flaws, e.g. so-called quadrant jumps in circles.
Further drawbacks arise with respect to the linear drives used in modern machine tools. Such linear drives/linear motors are only able to apply small holding forces so that a weight compensation as well as measures for the respective mounting are indispensable in the case of vertically movable components.